This invention relates to a composition and method for xe2x80x9cpost-addingxe2x80x9d cosmetic attributes to a fabric softening base composition at the final stage of its manufacture. More particularly it relates to a water-in-oil microemulsion which is suitable for containing adjuvants such as perfume or colorant and which can be readily mixed with a fabric softening base composition with only a minimum amount of shear and without adversely affecting its physical stability.
Perfumes and colorants are routinely introduced into liquid fabric softening compositions to provide appealing cosmetic attributes for the consumer. The introduction of perfume, for example, to a liquid softening composition, is meant to leave a pleasant and lasting fragrance on the treated fabrics. The colorant is intended to provide a visually pleasing product as well as convey to the consumer an overall impression of softness and quality. From a marketing standpoint, perfumes and colorants are attributes which allow the formulator a degree of flexibility to provide product variety for a given softening technology or for a fixed fabric softening base composition.
Although perfume, on a weight basis, is invariably a very minor component of a commercial fabric softener composition, its introduction into the composition in an efficient manner is a subject of much concern in the formulation art. This is particularly true for concentrated fabric softeners containing more than about 10% by weight of active softening ingredients insofar as the aqueous softener base compositions tend to gel in the presence of water-immiscible perfume. This tendency of gel formation is particularly problematic when the water-immiscible perfume is poorly dispersed in the aqueous emulsion which constitutes the softening base composition.
Undesirable thickening or gelation of a softener base composition has significant drawbacks: it reduces the effective shelf life of the final product and adversely affects consumer acceptance for a softener product which upon use has thickened to an unexpectedly viscous mass instead of meeting the consumers expectation of being essentially free-flowing. As a result the prior art has addressed itself to overcoming the pervasive problems of gelation and the formation of high viscosity liquids which accompany the introduction of water-insoluble perfumes into aqueous fabric softener base compositions.
U.S. Pat. No. 5,447,644 to International Flavors and Fragrances (IFF) describes a method to avoid gelation of the softening composition resulting from the introduction of increased levels of perfume into a softener base composition. According to this method there is first formed an aqueous microemulsion by mixing the perfume with a defined nonionic surfactant under conditions of high shear to uniformly disperse the perfume in the surfactant/water mixture. The perfume-containing microemulsion is then mixed with a fabric softener base formulation to form the final fabric softener composition. A high shear mixer is required for this mixing operation.
Accordingly, there remains a need in the art for a method to readily introduce fragrances and colorants into a fabric softener base at the very end of the manufacturing process or even by the consumer himself in the home under very gentle mixing conditions, avoiding the need for high shear mechanical agitation and equipment. Further, there is a need for a method which apart from incorporating perfume or colorants into a base formulation, will do so without adversely impacting the rheological and physical stability of the final product.
In accordance with the present invention there is provided a perfume-containing water-in-oil microemulsion capable of being mixed with a perfume-free fabric softener base composition which is in the form of an aqueous emulsion so as to disperse perfume in said aqueous emulsion under conditions of low shear while avoiding any problem of gelation to thereby provide a physically stable perfume-containing liquid fabric softening composition, said water-in-oil microemulsion comprising:
(a) from about 5% to about 80%, by weight, of a surfactant fabric softener selected from the group consisting of:
(i) diester quaternary ammonium compounds having the structural formulae as follows: 
xe2x80x83wherein each
A is independently C(O)Oxe2x80x94Rxe2x80x2 or xe2x80x94O(O)Cxe2x80x94Rxe2x80x2;
R is a lower alkyl group having 1 to about 4 carbon atoms;
Rxe2x80x2 is an alkyl or alkenyl group having 8 to about 22 carbon atoms;
Rxe2x80x3 is independently a lower alkyl radical having 1 to about 6 carbon atoms or hydroxyl alkyl group or H;
n is an integer having a value of 1 to about 3; and
Xxe2x88x92 is a softener compatible anion; and 
wherein B is independently A or (R)nxe2x88x92A; and A, R, Rxe2x80x3 and n are as defined above; and 
wherein A, R, Rxe2x80x3 and n are as defined above; and/or
(ii) diamido ammonium compounds having the formula: 
wherein n, Xxe2x88x92 and Rxe2x80x2 are as defined above, R1 is a lower alkyl radical having 1 to about 4 carbon atoms or hydrogen, and R is an alkylene radical having 2 to about 4 carbon atoms;
(b) from about 2% to about 50%, by weight, of an organic solvent;
(c) from about 15% to about 70%, by weight, of a water-immiscible perfume, components (a), (b) and (c) comprising the oily phase of said microemulsion;
(d) from 0% to about 1% of a colorant; and
(e) from about 0.5% to about 26%, by weight, of water; said microemulsion being free of an anionic surfactant, and having a weight ratio of said oily phase to water of from about 3:1 to about 200:1 with the proviso that for weight ratios of said oily phase to water of below 9:1, the weight ratio of perfume to solvent is less than 1:1; and/or the surfactant fabric softener (a) is greater than 25%, by weight, and wherein the percentages of components (a), (b) and (c) are selected so that the resulting composition forms a water-in-oil microemulsion.
Danielsson and Lindman, xe2x80x9cThe definition of Microemulsionxe2x80x9d, Colloids and Surfaces, 3 (1981), 391-392, Elsevier Scientific Publishing Company, have defined a xe2x80x9cmicroemulsionxe2x80x9d as xe2x80x98a system of water, oil and amphiphile which is a single optically isotropic and thermodynamically stable liquid solutionxe2x80x99. This definition of microemulsion is used herein in describing the present invention.
In accordance with the above definition, a microemulsion has the following characteristics/properties:
i) Clear
ii) It is free of lyotropic liquid crystalline system (i.e. it is isotropic)
iii) It has relatively low viscosity
iv) It is formed spontaneously by simple mixture/agitation of all components (i.e. it is thermodynamically stable)
More detailed information concerning various aspects of microemulsion systems such as definition, phase behavior, structure, low interfacial tensions and dynamics, is disclosed in R. Zana""s article, xe2x80x98Microemulsionsxe2x80x99 in Heterogeneous Chemistry Reviews, Vol. 1, 145-157 (1994), edited by John Wiley and Sons Ltd, the disclosure of which is incorporated herein by reference.
The present invention also provides a method for introducing a perfume into a perfume-free fabric softener base composition which is in the form of an aqueous emulsion under conditions of low shear and without adversely affecting its physical stability comprising the steps of:
(a) providing a perfume-containing water-in-oil microemulsion as defined above; and
(b) mixing an amount of said water-in-oil microemulsion sufficient to contain the desired amount of perfume with said fabric softener base composition under conditions of low shear thereby causing the inversion of said microemulsion and the dispersion of the perfume to form a physically stable perfume-containing liquid fabric softening composition.
The water-in-oil microemulsion compositions of the invention are predominantly comprised of the oily phase as defined above, namely, the cationic surfactant fabric softener, the organic solvent and the water-insoluble perfume. To form a composition in the desired phase of a water in oil microemulsion, the amount of water should generally be no greater than about 30%, by weight, and preferably, from about 5% to about 25%, by weight.
The preferred diester quaternary ammonium surfactants for use herein are the dioleyl diester xe2x80x9cquatsxe2x80x9d represented by equation (1). Particularly preferred is methyl bis-[ethyl(oleyl)]-2-hydroxyethyl ammonium methyl sulfate, commonly referred to as xe2x80x9cDODEQxe2x80x9d.
The present invention is predicated on the discovery that cosmetic attributes such as perfume and colorant can be readily xe2x80x9cpost-addedxe2x80x9d to an aqueous fabric softening base composition at the final stage of its manufacture by using a water-in-oil microemulsion as herein defined as the vehicle to be added to and mixed with the aqueous emulsion to form the finished product. The water-in-oil microemulsion is incorporated into the softening base composition under conditions of gentle agitation or low shear, using a sufficient amount to provide the desired level of perfume to the finished product. The microemulsion undergoes an inversion upon dilution in the aqueous emulsion which serves to efficiently disperse the perfume or colorant throughout the composition without concomitant problems of gelation or product instability.
Accordingly, the present invention provides important advantages from the standpoint of manufacturing a softening product composition as well as in insuring the integrity of the final product itself. The essence of the present invention is an oil in water microemulsion which can be readily formed at room temperature with no need for high shear forces or elaborate mixing equipment. And with regard to the finished product, it is clear that the introduction of cosmetic attributes into a softening base composition is accomplished without adversely compromising the rheology or physical stability of the resulting product.
Diester quaternary ammonium surfactant fabric softeners, represented by equation (1) are preferred for use herein and are commercially available from Stepan Co. as Stepantex and from KAO Corp. as Tetranyl but can also be synthesized by the reaction of two moles of a fatty acid with a trialkanolamine, preferably, triethanolamine followed by methylation with dimethyl sulfate or an alkyl halide such as, methyl iodide. In a preferred mode the fatty acid is oleic acid. For economical reasons it has been found that Soya fatty acids are a practical source for this purpose consisting of about 3% myristic acid, about 5% palmitic acid, about 5% palmitoleic acid, 1.5% stearic acid, 72.5% oleic acid and about 13% linoleic acid. Other sources of useful fatty acids are those obtained from the saponification of beef tallow, butter, corn oil, cottonseed oil, lard, olive oil, palm oil, peanut oil, cod liver oil, coconut oil and the like.
A preferred diester quaternary ammonium surfactant fabric softener is methyl bis[ethyl(oleyl)]-2-hydroxyethyl ammonium methyl sulfate. Other diesters useful in the practice of this invention include:
methyl bis-[ethyl(coconut)]-2-hydroxyethyl ammonium methyl sulfate
methyl bis-[ethyl(decyl)]-2-hydroxyethyl ammonium methyl sulfate
methyl bis-[ethyl(dodecyl)]-2-hydroxyethyl ammonium methyl sulfate
methyl bis-[ethyl(lauryl)]-2-hydroxyethyl ammonium methyl sulfate
methyl bis-[ethyl(palmityl)]-2-hydroxyethyl ammonium methyl sulfate
methyl bis-[ethyl(soft-tallow)]-2-hydroxyethyl ammonium methyl sulfate, and the like.
The designation of the terms coconut and soft-tallow indicate mixtures of esters corresponding to the fatty acid source.
In the preparation of the diester quaternary ammonium surfactants, a certain amount of the triester homolog may be produced as an impurity.
The term xe2x80x9cperfumexe2x80x9d is used herein in its ordinary sense to refer to and include any non water-soluble fragrant substance or mixture of substances including natural (i.e., obtained by extraction of flower, herb, blossom or plant), artificial (i.e., a mixture of natural oils or oil constituents) and synthetic (i.e., a single or mixture of synthetically produced substance) odoriferous substances. Typically perfumes are complex mixtures of blends of various organic compounds, such as, esters, ketones, hydrocarbons, lactones, alcohols, aldehydes, ethers, aromatic compounds and varying amounts of essential oils (e.g., terpenes) such as from about 0% to about 80%, usually from about 10% to 70% by weight, the essential oils themselves being volatile odoriferous compounds and also serving to dissolve the other components of the perfume. The precise composition of the perfume has no particular effect on fabric softening so long as it meets the criteria of water immiscibility and pleasant odor.
Organic solvents suitable for use in this invention include: aliphatic alcohols having 1 to about 6 carbon atoms, such as, ethanol, propanol, isopropanol, n-butanol, isobutanol, t-butanol, n-pentanol, isopentanol, sec-pentanol, n-hexanol, isohexanol, other isomers and the like; aliphatic polyalcohols, such as, ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, dipropylene glycol, 1,4-butanediol, 2-methyl-pentanediol, hexane triol, tripropylene glycol, pentaerythritol, glycerol, sorbitol, and the like; aliphatic ethers, such as, ethylene glycol monobutyl ether(EGMBE), diethylene glycol monobutyl ether(DEGMBE), diethylene glycol dimethyl ether, triethylene dimethyl ether, ethylene glycol monomethyl ether, propylene glycol monoethyl ether, dipropylene glycol monomethyl ether, dipropylene glycolpropyl ether(DPnP), dipropylene glycolbutyl ether(DPnB), tripropylene glycol monomethyl ether, methoxy methyl butanol, and the like; aliphatic esters, such as, methyl lactate, ethyl lactate, isopropyl lactate, butyl lactate, dibasic esters of carboxylic acids, ethoxy ethyl acetate, propylene glycol butyl ether acetate, and butoxy ethyl acetate.
Among the preferred organic solvents for use herein are dipropylene glycol methyl ether (DPM); dipropylene glycol monobutyl ether (DPnB); and ethylene glycol monobutyl ether (EGMBE).
In the water in oil microemulsion compositions in accordance with the invention, the weight range of cationic surfactant is generally from about 5% to about 80%, and preferably from about 10% to about 60%, by weight; the weight range of the organic solvent is generally from about 2% to about 50%, and preferably from about 4% to about 40%, by weight; and the weight range of the water-immiscible perfume is generally from about 5% to about 80%, and preferably from about 15% to about 70%, by weight. The water content is generally from about 0.5% to about 30%, and preferably from about 5% to about 26%, by weight. The weight ratio of the defined oily phase to water is generally from about 3:1 to about 200:1, preferably from about 5:1 to 50:1, and most preferably from about 5:1 to about 20:1 with the proviso that if the weight ratio of said oily phase water is below 9:1, then either or both of the following must occur in order to form a water-in-oil microemulsion composition: (i) the weight ratio of perfume to solvent must be less than 1:1; or (ii) the surfactant fabric softener must be greater than 25% by weight.
The microemulsions of the invention have a particle size between 10 and 100 nanometers. At particle sizes below about 50 nanometers, the microemulsions are generally clear. The microemulsions are formed by simply combining the above-described components of the composition under gentle agitation or low shear. Conventional mixing equipment known to those skilled in the art is sufficient for this purpose. All of the components described herein, both required and optional, must be normally liquid, namely, liquid at ambient room temperatures. Accordingly, there is no need for heating during the preparation of the microemulsions.
The invention is further described in the examples which follow. All parts and percentages are by weight unless otherwise specified.
Microemulsion compositions/area in a pseudo-ternary phase diagram (i.e. 4 components) were basically determined on a clear/turbid criteria basis by mixing three of the components and titrating with incremental amounts of the fourth component. Generally, 3.0 g of a mixture consisting of organic solvent (or mixture of), water-immiscible perfume and water, were introduced in a suitable/fixed ratio, and then titrated with DODEQ (dioleyl diesterquat). Samples were mixed at RT using a magnetic stirrer operating at 100-150 rpm after which they were allowed to stand for few minutes before visual examination for clarity/tubidity. Clear samples were further examined under a polarizing microscope to check that the liquids were isotropic. By this method, estimated regions for microemulsion compositions were located on pseudo-ternary phase diagrams. Some compositions located inside these microemulsion areas were selected to illustrate the present invention.